A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle carries a navigation function. Such a navigation system detects the position of the user or user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium in the navigation system. The navigation system displays a map image on a monitor screen while superimposing a mark representing the current location of the user on the map image. When a destination is set, the navigation system starts a route guidance function for setting a guided route from the start point to the destination and guides the user to the destination.
FIGS. 1A-1H show an example of overall procedure and screen display involved in the navigation system. FIG. 1A shows an example of locator map screen of the navigation system typically used when the destination is not specified. The navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. Other information such as a north pointer NP, a map scale and a current time may also be illustrated on the display screen.
FIGS. 1B-1F show an example of process for specifying a destination in the navigation system. When selecting a “Destination” menu on a main menu screen of FIG. 1B, the navigation system displays an “Find Destination By” screen as shown in FIG. 1C for specifying an input method for selecting the destination. The “Find Destination By” screen lists various methods for selecting the destination. This example includes the methods of “Address”, “Intersection”, “Point of Interest”, “Recent Route”, “Address Book”, and “Today's Plan” which are well known in the art.
When selecting, for example, the “Address” method in FIG. 1C, the navigation system displays a keyboard screen in FIG. 1D. Suppose the user inputs an address “2525 W. Carson” of a “Del Amo” shopping mall, the navigation system displays a “Confirm Destination” screen such as shown in FIG. 1E. If the name and address on the screen shows the correct destination, the user enters an “OK to Proceed” key to proceed to the next procedure.
In FIG. 1F, the navigation system calculates and determines a route to the destination, i.e., the address “2525 W. Carson”. The navigation system determines a route to the destination based on, for example, the quickest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. In this example, the navigation system displays a progress scale of the calculation of the route.
Once the route to the destination is determined, the navigation system starts the route guidance as shown in FIG. 1G for guiding the user to the destination. Typically, the navigation system shows the intersection which is highlighted to show the next turn and a direction of the turn. Such route guidance by the navigation system is also accompanied by voice instructions. By approaching every intersection to turn, the navigation system automatically displays the intersection guidance diagram to instruct the user which direction to turn at the intersection.
The navigation system measures a distance to the current destination to detect whether the destination is within a predetermined range such as within 100 meters. When the user approaches the destination within such a predetermined distance, the navigation system indicates that the destination “Dest” is ahead as shown in FIG. 1H. The navigation system detects the actual arrival based on various factors such as the engine stop.
In the foregoing process, the point which the navigation system indicates as the destination may not exactly be an actual position of the destination intended by the user. For example, in the conventional navigation system, the position of the destination calculated by the system sometimes does not match the actual position of the street address. This is because the map information usually shows only the address number and absolute position of each end of a street segment. Thus, the map data does not always include an accurate position of street address for each and every address number on the street.
Such a situation is shown in FIGS. 2A-2C. FIG. 2A shows the address distribution on a street segment of a particular street “2525 Carson W. Street” in FIGS. 1A-1H which is assumed by the navigation system. FIG. 2B shows an example of actual address distribution on the street segment of FIG. 2A. For example, as shown in FIG. 2A, the map data provides the street address number and its position of each end of a street segment. Thus, although the address number and position at each end (1000 and 4000) of the street segment are accurate, positions of intermediate addresses are not always accurate. This is because they are spread evenly by the navigation system, i.e., with a constant interval, along the street between the lowest address number and the highest number of the street segment. Thus, the address number “2525 Carson W. Street” in FIGS. 1A-1H is assumed to be at the location shown in FIG. 2A.
However, since the actual address numbers are assigned irregularly as shown in FIG. 2B, the actual position (arrival position) of the destination is different from the position of FIG. 2A by a distance d. Therefore, a user may be confused when the navigation system announces the arrival at the incorrect position on the street. FIG. 2C shows another example of actual address distribution where address numbers on the street in a residential area is proportionally assigned with relatively small interval while the address numbers on the street in a park, field or vacant land are assigned unevenly, i.e., by an irregular interval with relatively large interval.
Therefore, there is a need of a new navigation method system which is able to improve the performance in interpreting an address number of a destination based on the other information contained in the map database so that the actual position of the destination can be determined more accurately.